An inkjet printer typically includes one or more printheads and their corresponding ink supplies. A printhead includes an array of drop ejectors, each ejector consisting of an ink chamber, an ejecting actuator and a nozzle through which droplets of ink are ejected. The ejecting actuator may be one of various types, including a heater that vaporizes some of the ink in the chamber in order to propel a droplet out of the nozzle, or a piezoelectric device which changes the wall geometry of the chamber in order to generate a pressure wave that ejects a droplet. The droplets are typically directed toward paper or other recording medium in order to produce an image according to image data that is converted into electronic firing pulses for the drop ejectors as the print medium is moved relative to the printhead.
Ink is provided to the printhead through an ink inlet of the printhead. For the case of ink supplies that are mounted on the carriage of a carriage printer, the ink supply can be permanently mounted onto the printhead, so that the printhead needs to be replaced when the ink is depleted. Alternatively an ink tank can be detachably mounted onto the printhead, so that only the ink tank itself needs to be replaced when the ink tank is depleted. Carriage mounted ink tanks (also called on-axis ink tanks) typically contain only enough ink for up to about several hundred prints. This is because the total mass of the carriage needs to be limited, so that accelerations of the carriage at each end of the travel do not result in large forces that can shake the printer back and forth.
Ink must be supplied to the printhead at a proper pressure range relative to ambient pressure. If the pressure is not sufficiently negative relative to ambient pressure, ink will tend to drool out of the printhead nozzles. If the pressure is excessively negative, the ink chambers of the drop ejectors will not fill sufficiently rapidly, leading to printing misfires and degraded image quality. Typically, a pressure regulation mechanism, such as a capillary medium, or a spring-biased bag is included in the ink tank. Such pressure regulators within the ink tank take up space that could otherwise be occupied by ink. In addition, incorporating the pressure regulator within the ink tank adds cost to the ink tank and results in more material being discarded when the ink is depleted. Finally, the pressure regulator typically retains a quantity of ink, so that when no more ink can be delivered to the printhead and the ink tank must be replaced, there is still ink remaining.
What is needed is a printhead assembly having an on-axis replaceable ink tank having a more compact, low cost design that wastes less ink and is more environmentally friendly.